1. Field of the Invention
The present invention relates to a magneto-resistive element used for a magnetic head, a magnetic field sensor or the like, a magnetic head using the magneto-resistive element, a magnetic recording apparatus (magnetic recording and playback apparatus), and a magnetic memory.
2. Description of the Related Art
A multi-layer indicating a magnetic tunneling phenomenon is reported in Physics Letters, vol. 54A (1975), No. 3, p. 225 by Jullier. With higher density of magnetic recording, as a future playback magnetic head, application of the multi-layer to a magneto-resistive type head has been studied.
The multi-layer comprises a laminate having a magnetic layer, an insulating layer, and a magnetic layer laminated in the order, and when an electron issued from one magnetic layer and tunneling through the insulating layer enters the other magnetic layer, a change occurs in the tunneling probability depending on the direction of magnetization of two magnetic layers. The change in the tunneling probability is observed as a magneto-resistance.
Where the conventional multi-layer is used for the magneto-resistive element, it is necessary, when an external magnetic field is not present, to make the direction of magnetization of a magnetic layer magnetized and rotated by the external magnetic field substantially at right angles to the detecting direction of the external magnetic field. This is necessary for the reason that symmetry of playback outputs when the magneto-resistive element is applied to the external magnetic field is better. However, a leakage magnetic field from the other magnetic layer is applied to the magnetic layer magnetized and rotated by the external magnetic field, and the direction of magnetization is not at right angles to the detecting direction of the external magnetic field. The leakage magnetic field from the other magnetic layer delicately changes due to the construction of the magneto-resistive element, the thickness of the magenta layer, the unevenness of the insulating layer, and so on, thus posing a problem that controlling the direction of magnetization of the magnetic layer is difficult.
It is a first object to provide a magneto-resistive element which is excellent in symmetry of playback waveforms.
It is a second object of the present invention to provide a magnetic head using such a magneto-resistive element as described.
It is a third object of the present invention to provide a magnetic recording apparatus using such a magnetic head as described.
It is a fourth object to provide a magnetic memory which is excellent in symmetry of playback waveforms.
For achieving the aforementioned first object, according to the present invention, there is provided a magneto-resistive element comprising, a multi-layer having a first magnetic layer, an insulating layer, and a second magnetic layer laminated on a substrate in said order, a means for applying a voltage between the first magnetic layer and the second magnetic layer, a direction of magnetization of one magnetic layer of the first magnetic layer and the second magnetic layer being substantially parallel or counter-parallel with a detecting direction of an external magnetic field, a control means for making a direction of magnetization of the other magnetic layer of the first magnetic layer and the second magnetic layer substantially at right angles to the detecting direction of an external magnetic field when the external magnetic field is not present, and a means for detecting, when the direction of magnetization of the other magnetic layer is changed by the external magnetic field, a change of a current tunneling through the insulating layer caused thereby.
In the magnetic resistive element, if the direction of magnetization of the other magnetic layer is made completely at right angles to the detecting direction of the external magnetic field, playback waveforms are symmetrical, but if deviated from the right angles, the symmetry lowers. The substantially right angles termed herein means that if the non-symmetry of playback waveforms is in the range within 5%, the direction may be deviated from the right angles. This deviation is for example, approximately xc2x15 depending on the shape of the playback waveform.
Further, the terms xe2x80x9ca direction of magnetization of one magnetic layer being substantially parallel or counter-parallel with a detecting direction of an external magnetic fieldxe2x80x9d herein means that a deviation in the range similar to the direction of magnetization of the other magnetic layer is allowed to be parallel or counter-parallel. The same is true for the following description.
In the electro-resistive element, an anti-ferromagnetic layer is laminated on one magnetic layer, and the anti-ferromagnetic layer and one magnetic layer are subjected to magnetic exchange coupling to make the direction of magnetization of one magnetic layer substantially parallel or counter-parallel with the detecting direction of the external magnetic field.
In this case, as the control means, there can be provided a means for causing a current to flow in an inner direction of a layer surface of at least one layer of the anti-ferromagnetic layer and a crystal orientation control layer. Further, as the control means, there can be provided a means for causing a current to flow in an inner direction of a layer surface of the other magnetic layer, and a means for causing a current to flow in an inner direction of a layer surface of a non-magnetic metal layer laminated on a multi-layer.
Further, coercive force of one magnetic layer is made higher than that of the other magnetic layer, without providing the anti-ferromagnetic layer, and as the control means, there can be provided a means for causing a current to flow in an inner direction of a layer surface of a non-magnetic metal layer laminated on a multi-layer. Further, likewise, coercive force of one magnetic layer is made higher than that of the other magnetic layer, being arranged on a substrate and there is provided with a means for causing a current to flow in an inner direction of a layer surface of one magnetic layer.
Further, for achieving the aforementioned first object, according to the present invention, there is provided a magneto-resistive element comprising, a multi-layer having a first magnetic layer, a first insulating layer, a second magnetic layer, a second insulating layer, and a third magnetic layer laminated on a substrate in said order, a means for applying a voltage between the first magnetic layer and the third magnetic layer, a direction of magnetization of one magnetic layer of a set of the first and third magnetic layers and the second magnetic layer being substantially parallel or counter-parallel with a detecting direction of an external magnetic field, a control means for making a direction of magnetization of the other magnetic layer of the set of the first and third magnetic layers and the second magnetic layer substantially at right angles to the detecting direction of the external magnetic field when the external magnetic field is not present, and a means for detecting, when the direction of magnetization of the other magnetic layer is changed by the external magnetic field, a change of a current tunneling through the insulating layer caused thereby.
As the control means, there can be provided a means for making coercive force of one magnetic layer higher than that of the other magnetic layer, laminating a non-magnetic metal layer on a multi-layer, and causing a current to flow in an inner direction of a layer surface of the non-magnetic metal layer.
Further, anti-ferromagnetic layers are provided on both sides of a multi-layer, one magnetic layer comprising a set of the first and third magnetic layer, and as the control means, there can be provided a means for causing a current to flow in an inner direction of a layer surface of at least one layer of the anti-ferromagnetic layer and a crystal orientation control layer laminated on the side opposite to on the side in which a multi-layer of one of the anti-ferromagnetic layers is arranged.
Further, for achieving the aforementioned first object, according to the present invention, there is provided a magneto-resistive element comprising, a multi-layer having a hard magnetic layer, a non-magnetic metal layer, a first soft magnetic layer, an insulating layer, a second soft magnetic layer, and an anti-ferro magnetic layer laminated on a substrate in said order from the side closer to the substrate, a means for applying a voltage between the first soft magnetic layer and the second magnetic layer, the anti-ferromagnetic layer and the second soft magnetic layer being subjected to magnetic exchange coupling, a direction of magnetization of the second soft magnetic layer being substantially parallel or counter-parallel with a detecting direction of an external magnetic field by the exchange coupling, and a direction of magnetization of the first soft magnetic layer being made substantially at right angles to the detecting direction of an external magnetic field when the external magnetic field is not present, and a means for detecting, when the direction of magnetization of the first soft magnetic layer is changed by the external magnetic field, a change of a current tunneling through the insulating layer caused thereby.
Further, for achieving the aforementioned second object, according to the present invention, there is provided a magnetic head comprising a magneto-resistive type head for read, and an induction type head for write, the magneto-resistive element described in any one of the foregoing being used as the magneto-resistive type head.
Further, for achieving the aforementioned third object, according to the present invention, there is provided a magnetic recording apparatus comprising a magnetic recording medium, a magnetic head provided in correspondence with a recording surface of the magnetic recording medium, a driving unit for a magnetic recording medium, a driving unit for a magnetic head, and a recording and playback signal processing system, the afore-mentioned magnetic head (in the second object) being used as said magnetic head.
Further, for achieving the aforementioned third object, according to the present invention, there is provided a magnetic memory comprising a magneto-resistive element according to Embodiments 1, 2, 3 or 4 described later of the aforementioned magneto-resistive elements, and a magnetic field generating mechanism for directing a direction of magnetization of one magnetic layer at the desired direction. The magnetic memory may be provided with a means for heating a magneto-resistive element.
As described above, according to the present invention, a magneto-resistive element using a multi-layer in which two or three magnetic layers are separated by an insulating layer is used, an induction magnetic field is applied to a rotating magnetic layer magnetized by an external magnetic field, and the induction magnetic field applied to the magnetic layer is offset by a leakage magnetic field from a magnetic layer with magnetization fixed, as a result of which the magnetization of the magnetic layer is substantially at right angles to the magnetic field applying direction to thereby provide an excellent symmetry of playback waveforms.